This invention relates to a fluorescent lamp and a discharge lamp and more particularly to a fluorescent lamp that is suited for a light source for the backlighting liquid crystal displays that are used in various electronic devices such as personal computers, car-navigation displays, etc.
A fluorescent lamp is used as a light source for the backlighting of liquid crystal displays to irradiate uniform light to liquid crystal panels from the back in liquid crystal displays that are used in, for instance, personal computers or car-navigation displays. Accompanied with demands for large-sized, thin and high performance display area of liquid crystal displays, stable and sufficient light intensity, uniform distribution of luminance in the axial direction of lamp tube in the wide temperature range from xe2x88x9240xc2x0 C. to 85xc2x0 or under the control of light intensity from several % to 100%, are demanded for a fluorescent lamp itself as a light source for the backlighting jointly for small-sized luminance tube diameter and extended tube length.
However, because the light intensity of the conventional fluorescent lamp which contains mercury as discharge gas is insufficient at a low ambient temperature and mercury may cause the environmental pollution, the development of a fluorescent lamp without using mercury gas is demanded.
A small discharge lamp or a fluorescent lamp using inert gas such as neon gas, krypton gas or xenon gas is disclosed in Japanese Laid-Open Patent Publication (Kokai) No.57-63756. In this discharge lamp, one of two electrodes is provided in a glass tube and the other electrode is provided outside the glass tube. One of the electrodes is provided which extends along an almost entire length of a glass tube and the other electrode is provided on the outer surface of the glass tube against the electrode provided in the glass tube. It was disclosed that this lamp is a small discharge lamp with diameter of 2xcx9c10 mm and 50xcx9c200 mm long, which is used as a luminous display for displaying characters, numerals or symbols, in which a single lamp or plurarity of lamps having a straight or curved tube is or are used. It is also disclosed that such lamps are used as an energy-saving pilot lamp or a beacon light.
However, for the conventional discharge lamp or the fluorescent lamp in this structure, it is difficult to keep a uniform discharge distance from the inner electrode to the outer electrode along the overall length of the inner electrode and as a result, such problems are caused that a partial discharge is produced and a stable positive column cannot be formed on the entire length of a glass tube. In other words, since a slender fluorescent lamp using a glass tube of 1.6xcx9c10 mm in outer diameter and 100xcx9c500 mm in length, for example, is used for a backlighting source of a liquid crystal display, it is extremely difficult, in view of the manufacturing technology, to provide electrodes having a uniform discharge distance along the entire length of the glass tube.
Further, in a liquid crystal display, a fluorescent lamp is often subject to influence of vibration depending on the using condition and the inner electrode is deformed locally. Therefore, it is difficult to maintain a discharge distance at always constant value.
Furthermore, glass tubes having complicated shapes such as W or U-shaped tube may be often used for the backlighting sources in the liquid crystal displays. However, it is extremely difficult for the glass tube having such structure to form the electrodes having a uniform discharge distance between the inner electrode and the outer electrode along the entire length of them.
Further, even if a glow discharge region is formed along the entire length of the discharge lamp or the fluorescent lamp having the structure described above, there was a problem that electrons are actively emitted around an inner electrode and thus a diffused positive column is hardly formed thereby resulting a phenomenon that generation of ultraviolet rays is suppressed, in particular when a discharge medium containing xenon is used as discharge gas. Accordingly, when this type of the electrode structure is used for a fluorescent lamp having a glass tube inner wall of which is coated with phosphor for generatining luminance excited by ultraviolet rays, sufficient brightness cannot be obtained.
For the purpose of solving such problems involved in the conventional fluorescent lamps as described above, the applicant of the present invention filed an application as PCT/JP00/06491 (International Filing Date: Sep. 22, 2000) for a fluorescent lamp comprising a glass tube both ends of which are sealed airtight and filled with a discharge medium; a phosphor layer formed on an inner surface of the glass tube; an inner electrode arranged at one end of the glass tube and being given a electric potential; and an outer electrode composed of a conductor spirally wound round the glass tube between the both ends along an axis the tube at a prescribed pitch and being given with another electric potential.
It is an object of the present invention to provide a discharge lamp or a fluorescent lamp which are capable of stably emitting sufficient bright light for the entire length of a glass tube composing the discharge lamp by further improving the invention described above.
It is a further object to provide a discharge lamp or a fluorescent lamp capable of stably emitting light in an uniform luminance distribution for the overall length of a glass tube composing the discharge lamp or the fluorescent lamp.
A fluorescent lamp according to the present invention comprises a glass tube having both ends sealed airtight and containing a discharge medium filled therein, a fluorescent layer formed on the inner wall of the glass tube, an inner electrode arranged at one end of the glass tube which is given with one electric potential, and an outer electrode composed of a linear conductor spirally wound around the glass tube between its both ends at a prescribed pitch along an axis of the tube and is given with another electric potential, the outer electrode is so designed as to satisfy the formula:
wxc3x97nxe2x89xa60.3
where w(cm) is a width of the conductor comprising the outer electrode and n(turns/cm) is the average number of turns of the conductor in the unit length in the axial direction of the glass tube.
Further, a fluorescent lamp according to the present invention comprises a glass tube with a phosphor film formed on the inner surface thereof and with sealing portions so formed at each end thereof that a discharge medium is filled therein, a first feeding lead wire penetrating one of the sealing portions of the glass tube airtight, an inner electrode connected to an end of the feeding lead wire extending into the glass tube, a second feeding lead wire composed of a linear conductor which is spirally wound around an outer surface of the glass tube along an axial direction of the glass tube and an end of which is electrically connected to the second feeding lead wire, wherein the outer electrode is so designed that a winding pitch of the linear conductor becomes continuously or step wisely small corresponding to a distance from the inner electrode in the axial direction of the glass tube.
Further, a fluorescent lamp according to the present invention comprises a translucent tube with sealing portions formed at its both ends, a phosphor film formed on an inner surface of the translucent tube, a discharge medium containing rare gas filled in the translucent tube, a first feeding lead wire penetrating one of the sealing portions of the translucent tube and sealed therein airtight, an inner electrode provided at an end of the first feeding lead wire, and an outer electrode composed of a linear conductor which is spirally wound around the translucent tube for almost entire length of the tube in its axial direction and an end of which is connected to the second feeding lead wire, wherein the outer electrode is provided with a tube power increasing means at a portion where a disturbed diffused positive column or a constricted positive column is generated in the translucent tube when the fluorescent lamp is operated.
Further, in the fluorescent lamp according to the present invention, a winding pitch of the spirally wound linear conductor at the tube power increasing means is smaller than the winding pitch at the portion facing an adjacent diffused positive column.
Further, the fluorescent lamp according to the present invention comprises a long and slender translucent airtight container, a phosphor film formed on an inner surface of the translucent container, an inner electrode provided in the translucent airtight container, a discharging medium primarily composed of rare gas filled in the translucent airtight container, and an outer electrode composed of a conductive coil which is substantially in contact with an outer surface of the translucent airtight container extending along its longitudinal direction apart from the inner electrode and which enables to generate discharge in the translucent container between the outer electrode and the inner electrode, wherein the outer electrode containes at least one point of inflection where the winding pitch of the coil change from a small value to a large value.
Further, a fluorescent lamp according to the present invention comprises along and slender translucent air tight container, a phosphor film formed on the inner surface of the translucent container, a pair of inner electrodes sealed in the translucent container at both ends, a discharge medium primarily composed of rare gas filled in the translucent airtight container, and an outer electrode formed with a linear conductor coil which is wound around the outer surface of the translucent airtight container along a longitudinal direction of the translucent airtight container at a prescribed pitch and which generates the discharge between the outer electrode and the pair of inner electrodes, wherein a winding pitch of the outer electrode becomes minimum in a region pH facing a pair of constricted positive columns PCs generated in the translucent airtight container when the fluorescent lamp is in operation, becomes maximum at both ends in a region pV facing a diffused positive column PCd generated in the translucent airtight container, and decreases step wisely from the both ends toward the central portion.
Further, a discharge lamp according to the present invention comprises a translucent tube having sealing portions formed at its both ends and being filled with a discharge medium, an inner electrode which is arranged at one end of the translucent tube and is given with an electric potential, and an outer electrode which is composed of a linear conductor which is spirally wound around the translucent tube between the both ends along an axis of the translucent tube at a prescribed pitch and is given with another potential, wherein the outer electrode is so designed as to satisfy the formula:
wxc3x97nxe2x89xa60.3
where w(cm) is the width of the linear conductor forming the outer electrode and n(times/cm) is the average number of turns of windings per unit length in the axial direction of the translucent tube.
Further, a discharge lamp according to the present invention comprises a long and slender translucent tube having sealing portions formed at both ends so as to fill with a discharge medium within the translucent tube, a first feeding lead wire penetrating airtight one of the sealing portions of the translucent tube, an inner electrode connected to the end of the feeding lead wire at a portion extended into the translucent tube, and an outer electrode composed of a linear conductor which is spirally wound around the outer surface of the glass tube in the axial direction of the tube and an end of which is electrically connected to a second feeding lead wire, wherein the outer electrode is so designed that a winding pitch of the linear conductor becomes small continuously or stepweisely in an axial direction of the translucent tube corresponding to a distance from the inner electrode.
Further, a discharge lamp according to the present invention comprises a translucent tube having sealing portions formed at its both ends, a discharge medium including rare gas filled in the translucent tube, a first feeding lead wire sealed penetrating airtight one of the sealing portions of the translucent tube, an inner electrode provided at an end of the first feeding lead wire, and an outer electrode composed of a linear conductor which is spirally wound around the translucent tube for almost entire length in an axial direction of the tube and an end of which is connected to a second feeding lead wire, wherein the outer electrode is provided with a tube power increasing means a ta portion facing a disturbed diffused positive column or a constricted positive column generated in the translucent tube when the discharge lamp is in operation.
Further, a liquid crystal backlighting device according to the present invention comprises a main body of the liquid crystal backlighting, a fluorescent lamp arranged in the main body and a lighting circuit to operate the fluorescent lamp.